1. Field of the Invention
The present invention relates to a color filter suitable for use in color liquid crystal displays used in color televisions, personal computers, and the like, a production process thereof, and a liquid crystal panel, and particularly to a production process of a color filter for liquid crystals making good use of an ink-jet recording technique. The present invention also relates to a color filter for liquid crystals, which is produced by using the ink-jet recording technique, and a liquid crystal panel equipped with the color filter.
2. Related Background Art
With the advancement of personal computers, particularly, portable personal computers in recent years, the demand for liquid crystal displays, particularly, color liquid crystal displays tends to increase. It is however necessary to reduce the cost of the color liquid crystal displays for further spreading them. There is an increasing demand for reduction in the cost of color filters particularly given much weight from the viewpoint of the cost.
Various methods have heretofore been attempted for meeting the above demand while satisfying properties required of the color filters. However, no method satisfying all the required properties is yet established. The individual methods will hereinafter be described.
The first method oftenest used is a dyeing process. In the dyeing process, a sensitizing agent is added to a water-soluble polymeric material, which is a material for dyeing, to sensitize the polymeric material. The thus-sensitized polymeric material is applied on a glass base. After the coating film thus formed is patterned in the desired form by a photolithography process, the glass base on which the coating film has been patterned is immersed in a dye bath to obtain a colored pattern. This process is repeatedly performed three times to form colored layers of red (R), green (G) and blue (B).
The second method oftener used is a pigment dispersing process which has been replacing the dyeing process in recent years. In this process, a layer of a photosensitive resin in which a pigment has been dispersed is first formed on a base and then subjected to patterning, thereby obtaining a pattern of a single color. This process is repeatedly performed three times to form three colored layers of R, G and B.
As the third method, there is an electrodepostion process. In this process, a transparent electrode is first patterned on a base. The base is then immersed in an electrodeposition coating fluid containing a pigment, resin, electrolytic solution and the like to electrically deposit the first color. This process is repeatedly performed three times to form colored layers of R, G and B. Finally, the colored layers are calcined.
As the fourth method, there is a printing process in which three coatings of red, green and blue colors, each comprising a thermosetting resin and a pigment dispersed therein, are separately coated by repeated printing, and the resin to become a colored layer is then thermoset to form the colored layers. It is general to form a protective layer on the outermost colored layer in each process.
The need of repeating the same process three times to form the colored layers of R, G and B is common to these processes. Therefore, the cost is necessarily increased. There is also offered a problem that a yield is reduced as the number of processes increases.
In the third process by the electrodeposition, besides, formable patterns are limited. It is hence difficult to apply this process to a TFT color liquid crystal display in the existing technique. The fourth process involves a drawback that resolution and smoothness are poor, and is hence unfit to form a fine-pitch pattern.
In order to improve these drawbacks, Japanese Patent Application Laid-Open Nos. 59-75205, 63-235901, 1-217302 and 4-123005 each describe processes for producing a color filter by using an ink-jet system.
These processes are different from the above-described conventional processes. In these processes, coloring solutions (hereinafter referred to as inks) separately containing coloring matters of R, G and B are jetted out from respective nozzles on a filter base, and the inks are dried on the filter base to form colored layers. According to these processes, the formation of the individual colored layers of R, G and B can be performed at once, and moreover the amount of the inks to be used is saved. Therefore, they have effects of enhancing productivity to a great extent and reducing the cost.
However, these conventional processes have involved a major problem in technique that since pixels are formed by jetting out droplets of the liquid inks, it is difficult to apply the ink droplets to the desired positions of ink-droplet impact, for example, in the vicinity of the centers of the respective pixels of R, G and B, with precision, and so a problem of positional deviation in ink dots is easy to arise. When such positional deviation in ink dots occurs, a so-called blank area-shining phenomenon (a phenomenon that a transparent base looks brightly shining at its exposed position) occurs at a portion of a light-transmitting area, which is covered with no colored layer. Therefore, the definition of an image formed through the resulting color filter is reduced to a great extent. There is thus a demand for rapid establishment of a method for solving such a problem.
Japanese Patent Application Laid-Open No. 5-142407 describes a process for forming a color filter, in which pixel-forming materials are flowed in the form of a fluid out of minute nozzles, as a technique of concurrent multicolor printing. In such a process, however, colored stripes to be formed from the pixel-forming materials are continuously flowed out of the minute nozzles, so that the width and thickness of the colored stripe are varied according to variation in the outflow rate. In particular, when the variation in the outflow rate is wide, the colored stripe is torn off in the course of the outflow, so that the above-described blank area-shining phenomenon occurs. In order to prevent the tearing of the colored stripe, this method requires to lower the outflow rate of the pixel-forming material, so that the productivity also becomes poor.